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Re: Help Using XML::Parser module

by zakb (Pilgrim)
on Jun 11, 2003 at 12:00 UTC ( #265006=note: print w/replies, xml ) Need Help??


in reply to Help Using XML::Parser module

The basic premise for XML::Parser is that you define subroutines which get called when a start tag is found, an end tag is found or character data (i.e. between two tags) is found.

From your question, it looks like you need some help with the subroutines.

The three variables $p, $elt, %atts in the tutorial are defined as follows:

sub hdl_start{ my ($p, $elt, %atts) = @_; return unless $elt eq 'message'; # We're only interrested in wh +at's said $atts{'_str'} = ''; $message = \%atts; }

This snippet defines a subroutine called hdl_start. It gets called whenever the parser discovers a start tag (like <chatter>. The parser passes three parameters to the subroutine in the array @_. The first line in the subroutine (my ... then extracts those parameters from the array into the $p, $elt, %atts variables. The documentation for XML::Parser tells us that the parameters are:

Start (Expat, Element [, Attr, Val [,...]])
  • Expat ($p) is a reference to the underlying Expat XML parser.
  • Element ($elt) is the name of the element found - e.g. chatter
  • Attr, Val (%atts) are attribute / value pairs found as part of the start tag

So, to use a bit of the XML from the tutorial: <INFO site="http://perlmonks.org" sitename="Perl Monks">

  • $elt would contain 'INFO'
  • %atts would contain
    site => 'http://perlmonks.org' sitename => 'Perl Monks'

I think perhaps you may want to read some of the other Tutorials and may want to invest in the "Learning Perl" (llama) book. Tackling Perl and XML::Parser as your first project may be a little ambitious!

Replies are listed 'Best First'.
Re: Re: Help Using XML::Parser module
by bobn (Chaplain) on Jun 12, 2003 at 04:51 UTC
    I've used XML::Parser for several projects (I started before reading the tutorials that said it was too hard), and once you get used to the event driven model, it's not really difficult at all - especially if you control the XML format, too. Example: All info in attributes can really make life easy.

    --Bob Niederman, http://bob-n.com

      The problem with XML::Parser is not so much that it is hard to use, although it is quite convoluted in places. The problem is that SAX is a standard alternative to its streaming mode, and that XML::LibXML is a way better alternative to its tree mode. Plus XML::Parser is not actively maintained at the moment, which is always a problem when a new version of Perl, or of expat (the underlying library) comes out.

      So if you need to work in stream mode, your time will be better spent learning SAX, and if you are looking for convenience then XML::Simple, XML::LibXML or XML::Twig (or any of a number of other modules) are certainly better choices.

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